Tharsis Montes

A region on Mars from which four giant shield
volcanoes rise. Three of these volcanoes can be seen in the photo above.
They are Arsia Mons in the lower left, Pavonis Mons in the middle, and Ascreus
Mons in the upper right. The largest volcano of all on Mars (and in the
solar system), Olympus Mons, is also
in the Tharsis Region and lies off the image to the upper left.

Arsia Mons, Pavonis Mons, and Ascreus Mons dominate the center of the Tharsis
region, forming a line nearly 1500 km long. They are about equally spaced,
nearly 700 km apart, and reach a similar altitude to Olympus Mons, that
is, 25–26 km. However, the volcanoes of the Tharsis region sit on
a large mound of lava flows nearly 10 km high, so their true height is "only"
about 15 km. All three seem to have formed at about the same time and were
active for a long period. Arsia Mons appears to be slightly older than Pavonis
Mons, which, in turn, slightly predates Ascreus Mons, indicating that volcanism
in the Tharsis region gradually shifted north over time. A similar progression
of volcanism is found in the Hawaiian Islands. Almost certainly, the giant
shield volcanoes on Mars formed over a hotspot in the mantle as did their
Hawaiian counterparts.